When there was no satellite connection: SOS antennas launched by kites

Imagine this picture – your plane crashed somewhere in the sea. You managed to escape thanks to a vest and a lifeboat. Now this is not a very big problem – you can get a satellite phone (if it survived, of course) and call the appropriate service. But during World War II, there were no such phones. But the military had special emergency radio stations.

We are talking now about the military of the United States and Great Britain, who took the idea from the Germans (approx. Transl. – if at that time the USSR had something similar – write in the comments, please). Despite the fact that these systems are almost a century old, we can still see how the developers of that time tried to solve the problems that arose. How, for example, sitting in the same boat, can you deploy an antenna 90 meters long? The answer is with a kite. Well, or a ball of hydrogen.

Why such a long antenna?

In those days, the emergency frequency was a radio frequency of 500 kHz. This solution allowed simple spark gap transmitters to be placed on lifeboats even in the 1920s. But the wavelength of this range was about 600 meters. A quarter-wave antenna capable of operating in these ranges was 150 meters long.

After the sinking of the Titanic, an emergency frequency of 500 kHz became standard. Even after the spark gaps went out of mass use, spark gaps continued to be left in the inventory of lifeboats – simply because of their simplest design. By the beginning of the war, it was the 500 kHz frequency that became emergency.

A bit of history

The German NS2 (or NSG2) system was a 500 kHz dual-tube transmitter with a crystal oscillator. After the outbreak of World War II, the British managed to capture one of them. Having studied NS2, the British military created their own transmitter, which was named the T-1333. The Americans received a second copy of the same system around the same time. They developed on the basis of the German SCR-578 device and its “descendant” – BC-778. And just the 578th model had a special metal frame for preparing a box kite. Moreover, the Americans also added a special balloon with a hydrogen generator for it.

^{Box kite used by the German military to raise the antenna to the required height}

The generator made it possible to obtain hydrogen directly from water – more on that below. The balloon was filled with hydrogen, which rose and pulled the antenna behind it. The range of a 4.8W transmitter with an antenna length of 90 meters was 320 km. In order for the transmitter to work somehow, an antenna 53 meters long was enough.

The kite and ball were the only possible solution for raising the antenna to a height of almost 100 meters. The antenna was wound on a coil, it also served as a tool for controlling the kite. Everything was well thought out – it is obvious that the developers of this system have repeatedly tested it, imagining the conditions in which a person finds himself in a boat swaying on the waves. The shape of the body of the radio transmitters was such that the device could be squeezed between the knees during operation – it resembled an hourglass. Thanks to this form, the system even had its own name “Gibson Girl”. Moreover, the devices were waterproof and stayed in the water, rather than drowning when hit.

The system options were different. So, NSG2 gave out 8 watts using a crystal oscillator. But the version from the US military did not have a crystal and, accordingly, was low-power. The British model T1333 had a special flare kit for the initial launch of the kite. It rose to a height of about 60-70 meters, where the kite was laid out. This model did not have a balloon.

All this pleasure weighed a lot – about 15 kg. But, as mentioned above, the radio transmitters did not sink. The US transmitters included a warning light, two balloons, two hydrogen generators, two sets of antennas, and a parachute so that it could all be dropped from an aircraft.

Safe as a Swiss watch

The system designers tried to foresee everything. It is clear that a military man who had an accident and was forced to somehow survive on the high seas would be very upset by the fact that the batteries of the radio transmitter have run out. For this simple reason, there were no batteries, but there was an electricity generator – it was enough to twist the handle to “start” the device. If there was enough strength to twist the handle, a distress signal could be given.

By the way, the generator did not run on electrolysis. It contained lithium hydride, which reacted with water to produce hydrogen as a chemical reaction product. The system also transmitted SOS in automatic mode, and, of course, without any electronics or microcontrollers, before the invention of which there were still many decades.

The design turned out to be so reliable and durable that military and civilian aircraft were equipped with the SCR-578 or its direct descendant AN / CRT-3 until the 1970s. The new model was able to work with a frequency of 8364 kHz.

Everything for the user

The radio system described in this article was almost perfect – everything was thought out in it, to the smallest detail. Unfortunately, it is not known which of the German engineers developed the original NS2, but it was a person or a team who understood the practical issues of using such systems. The shape of the device allows you to easily hold it on a wobbly boat, the generator handle allows you to receive energy, the radio system works flawlessly. I wonder what other options were there for raising the antenna, before the developers settled on a combination of a balloon and a kite. Also, I wonder why the British military decided to stick with the flare and flare gun.

We can say that NS2 was one of the most sophisticated systems of its time. By the way, the forerunner of NS2, the system called NS1, was equipped with an inconvenient antenna, which was supposed to be used without auxiliary tools. In addition, it was powered by batteries. Most likely, the NS1 developers received feedback on their system and after that were able to design the NS2, which is an example of practicality in our time.